Study on the whitening effect and mechanism of alkali-additive-enhanced roasting on low-whiteness barite

To increase the utilisation and added value of low-whiteness barite, this study developed-for the first time-a whiteness enhancement method based on an alkali additive (Na 2 B 4 O 7 ·5H 2 O-Na 2 CO 3 ) and optimised the roasting process for removing impurities via single-factor experiments and response surface methodology. Various characterisation techniques, such as X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, thermogravimetry–differential scanning calorimetry and backscattered electron scanning electron microscopy, were employed to analyse and compare the physical and chemical properties of raw barite mineral as well as conventionally roasted and intensively roasted samples. In addition, the influence of the alkali additive on impurity removal during the intensive roasting of barite and the underlying whitening mechanism were investigated. Experimental results showed that roasting at 896 °C for 2.33 h with an alkali additive-raw barite mineral mass ratio (m Na2B4O7 · 5H2O :m Na2CO3 :m barite ) of 0.60:0.60:20 increased barite whiteness from 26.0 % to 95.7 %. The proposed method mainly involved using the alkali additive in the molten state to capture insoluble impurities (e.g. quartz, dolomite, calcite, and kaolinite) in the mineral samples at high temperatures. Furthermore, it generated borates, sodium compounds, and alkaline silica-aluminium salts (which were more easily soluble in sulphuric acid) and finally removed them via acid leaching and washing processes, further enhancing the whiteness of the mineral samples.